The present invention relates to a color solid-state imaging device in which a large number of photoelectric conversion elements for the three primary colors (red, green, and blue) and scanning circuits for deriving optical information from the respective elements are integrated on a semiconductor substrate.
A solid-state imaging device requires an imaging plate which has a resolution power equivalent to that of a pickup tube used in television broadcast equipment. Therefore, such a device needs photoelectric conversion elements which constitute a matrix of about 500.times.500 picture elements, switches for selecting (x,y) coordinates which correspond to the picture elements, an x (horizontal) scanning circuit, and a y (vertical) scanning circuit which turn the switches "on" and "off" and each of which consists of about 500 stages.
Accordingly, the solid-state imaging device ordinarily has a configuration as shown in FIG. 1. It is fabricated in accordance with MOS (metal-oxide-semiconductor) LSI (Large Scale Integration) circuit technology which can provide a high density of integration comparatively easily. Referring to FIG. 1, numeral 1 designates a horizontal scanning circuit for selecting x positions, while numeral 2 indicates a vertical scanning circuit for selecting y positions on the matrix. Numeral 3 represents a vertical switch MOS transistor (hereinbelow, simply termed "vertical switch") which is turned "on" or "off" by a scanning pulse from the circuit 2, numeral 4 a photodiode (photoelectric conversion element) which exploits the source junction of the vertical switch 3, and numeral 5 a vertical signal output line to which the drains of the vertical switches 3 are connected in common. Shown at 6 is a horizontal switch MOS transistor (hereinbelow, simply termed "horizontal switch") which is turned "on" or "off" by a scanning pulse from the horizontal scanning circuit 1, the drain of which is connected to a horizontal signal output line 7 and the source of which is connected to the vertical signal output line 5. Numeral 8 designates a photoelectric conversion element-biasing power source (usually called a "target power supply") which is connected to the horizontal signal output line 7 through a resistor 9. A common feature of solid-state imaging plates is that, since the individual picture elements are separate and scanning is executed by clock pulses externally impressed, the picture element whose signal is being read out can be readily discriminated. The solid-state imaging device is, accordingly, very convenient for obtaining color signals since the clock pulse serves as an index signal and because signals can be separated for the respective picture elements.
In the case of constructing a color television camera by the use of the solid-state imaging device in FIG. 1, three imaging plates for respectively converting lights of red (R), green (G), and blue (B) into electric signals are generally required. A color television camera employing the three solid-state imaging plates, however, needs a color resolving optical system for resolving image light into the three elementary colors of R, G, and B, a special imaging lens, etc. This forms a serious hindrance to the miniaturization of the camera and the reduction of its cost.
In view of this problem, a method has been proposed wherein, as illustrated by way of example in FIG. 2, the photoelectric conversion elements constituting a matrix of imaging picture elements are caused to correspond with color filters R, G, and B which transmit only red light, green light, and blue light respectively and which are arranged in a checkered pattern, whereby the three elementary color signals are derived from the single imaging plate (refer to the Official Gazette of Japanese Laid-Open Patent Application No. 51-112228). The expression "checkered pattern" signifies a pattern in which a plurality of color filters R, G, and B are arranged respectively periodically in the vertical and horizontal directions. The pitch of the array is not restricted to that illustrated in FIG. 2. In the construction shown in FIG. 2, the filters for green (or filters which transmit brilliance signals) are arranged horizontally and vertically on the imaging plate in a manner to fill up the interstices among the color filters of R and B. Therefore, even where the number of picture elements of the solid-state imaging plate is small, a color solid-state imaging device whose resolution is only slightly degraded can be provided. The method is very excellent for a system in which color signals are derived from a single solid-state imaging plate.
In principle, a color imaging device can be realized by combining the solid-state imaging device as shown in FIG. 1 and the color filters arranged in the checkered pattern as shown in FIG. 2. By this simple combination, however, the required demodulator becomes complicated, the processing of signal outputs is difficult and the expected high resolution cannot be attained.
Although, in FIG. 1, the principal construction is illustrated in order to explain the operation of the solid-state imaging device, in practice an interlaced scanning is required in the vertical direction in conformity with the display system of a pickup tube device. Moreover, for the purpose of preventing a capacitance lag (charges left unread), it is necessary to adopt an interlacing system in which two rows of picture elements are simultaneously selected (refer to the Official Gazette of Japanese Laid-Open Patent Application No. 51-57123). In the case of simultaneously selecting two rows of picture elements, by merely improving the vertical scanning and driving method of the solid-state imaging device shown in FIG. 1 (refer to the specification of Japanese Patent Application No. 51-71142), the color signals of the system employing the color filters shown in FIG. 2 cannot be read out in a manner to be separated for the respective picture elements. The reason therefor is that the signals of the two rows of picture elements simultaneously selected by the interlacing are delivered to the vertical signal output line 5 at the same time, so that both the signals mix with each other.